Air traffic control systems track positions and velocity of aircraft and help prevent aircraft collisions. Air traffic control has traditionally been based on radar surveillance, supplemented more recently with cooperative radio surveillance techniques, such as automatic dependent surveillance-broadcast (ADS-B). An aircraft may determine its own position, such as via a Global Navigation Satellite System (GNSS), and periodically broadcast its position via a radio frequency, which may be read by ground stations and other aircraft. Aircraft position data may be provided to a variety of other applications that serve functions such as traffic situational awareness, traffic alert, and collision avoidance, for example. As a particular example, an aircraft may be equipped with a Traffic Collision Avoidance System (TCAS) unit.